The correct localization of proteins within the various cellular compartments is of critical importance to the normal functioning of the living cell. The process of protein export has been intensively studied during the last decade. For gram-negative bacteria, the problem can be simplified by considering a limited set of compartments: a) the cytoplasm, b) the cytoplasmic membrane, c) the periplasmic space, d) the outer membrane and e) the extracellular milieu. Little is known as to the molecular mechanisms by which bacteria secrete biologically active peptides into the medium. The long term objectives of the proposed work are to characterize at the molecular level the steps leading to the export of two peptides produced by strains of E. coli. These peptides possess antibiotic activity and appear to be exported from the cell via novel export pathways. To achieve these goals, we propose to determine the pathway of maturation of the peptides as they go from intracellular precursors to extracellular active forms. This will be accomplished using a combination of biochemical and genetic approaches. Immunoprecipitation of labelled intermediates which accumulate in a variety of mutants defective in peptide export will provide the evidence for this pathway. Protein fusions will be generated to determine the topology of a putative membrane protein involved in peptide export. A collection of single amino acid replacements in the forty-three amino acid peptide will be generated. Biochemical analysis of these mutant forms will provide information that will relate the structure of the peptide to its various functions.